The present invention is directed toward a novel catalytic composite for the conversion of hydrocarbons and especially for effecting the dehydrocyclization of aliphatic hydrocarbons to aromatics. More particularly, the novel catalytic composite enables the conversion of C.sub.6 -plus paraffins to their corresponding aromatics with a high degree of selectivity thereby enabling the facile production of large quantities of aromatics.
In the past it has become the practice to effect conversion of aliphatic hydrocarbons to aromatics by means of the well-known catalytic reforming process. In catalytic reforming a hydrocarbonaceous feedstock, typically a petroleum naphtha fraction, is contacted with a Group VIII-containing catalytic composite to produce a product reformate of increased aromatics content. The naphtha fraction is typically a full boiling range fraction having an initial boiling point of from 50.degree. to about 100.degree. F. and an end boiling point of from about 325.degree. to about 425.degree. F. Such a full boiling range naphtha contains significant amounts of C.sub.6 -plus paraffinic hydrocarbons and C.sub.6 -plus naphthenic hydrocarbons. As is well known these paraffinic and naphthenic hydrocarbons are converted to aromatics by means of multifarious reaction mechanisms. These mechanisms include dehydrogenation, dehydrocyclization, isomerization followed by dehydrogenation. Naphthenic hydrocarbons are converted to aromatics by dehydrogenation. Paraffinic hydrocarbons may be converted to the desired aromatics by dehydrocyclization and may also undergo isomerization. Accordingly then, it is apparent that the number of reactions taking place in a catalytic reforming zone are numerous and, therefore, the typical reforming catalyst must be capable of effecting numerous reactions to be considered usable in a commercially feasible reaction system.
Because of the complexity and number of reaction mechanisms ongoing in catalytic reforming, it has become a recent practice to attempt to develop highly specific catalysts tailored to convert only specific reaction species to aromatics. Such catalysts offer advantages over the typical reforming catalyst which must be capable of taking part in numerous reaction mechanisms. In view of this, ongoing work has been directed toward producing a catalyst for the conversion of paraffinic hydrocarbons, particularly having six carbon atoms or more, to the corresponding aromatic hydrocarbon. Such a catalyst can be expected to be much more specific with respect to the final product compounds, resulting in fewer undesirable side reactions such as hydrocracking. As can be appreciated by those of ordinary skill in the art, increased production of aromatics is desirable. The increased aromatic content of gasolines, a result of lead phase down, as well as demands in the petrochemical industry make C.sub.6 -C.sub.8 aromatics highly desirable products. It is, therefore, very advantageous to have a catalytic composition which is highly selective for the conversion of less valuable C.sub.6 -plus paraffins to the more valuable C.sub.6 -plus aromatics.